This invention relates to a so-called in-line sealer of a type commonly used to apply heat seals to the upwardly facing openings in containers as an in-line operation.
Devices of this general type typically include a means for feeding a container-engaging pocket wheel which conveys the line of containers in a circular path during which time overlying vacuum heads receive a usually circular foil seal having a thermoplastic adhesive from a supply source and apply it to overlie the mouth of the container. The containers progress through a heated area which activates the adhesive, for effecting a seal on the container mouth, as the vacuum in the head is released, following which the containers are transferred to another moving means for transferring the now sealed containers to another location. Reference is made to my prior U.S. Pat. No. 4,816,110 granted Mar. 28, 1989, and my joint U.S. Pat. No. 4,719,739 granted Jan. 19, 1988 which discloses the above-described structure.
In accordance with the earlier patent, the sealing head picks up an individual seal from a source of supply and transfers it to the mouth of the container. Dwell means is provided to allow the vacuum head to dwell momentarily at the supply point without interrupting the continuous movement of the container. In the latter patent, the disclosed device includes separate supply means in the form of a vertical stack associated with each of the vacuum heads at a location which accesses the lowermost seal in the stack to the vacuum head. In both cases, heat is supplied externally by passing the containers through a heated area or tunnel.
While not without substantial utility, both of the above-described devices are not without significant shortcomings. In the case of a stacked seal supply, the supply must be manually replaced after a relatively short period of time, resulting in periodic shutdown. Normally, there is a stack associated with each head, and the usual practice is to replace all of the stacks at the same time.
A further problem has existed in the manner in which individual seals are picked up from the seal supply source. The prior art includes means for holding arcuate movement of the sealing head momentarily at the instant the seal is engaged. However, the prior art means does allow a small degree of radial movement which occasionally results in offset seals.
The use of a heated area or enclosure to activate the thermoplastic adhesive on the seals is relatively inefficient, since a much larger area adjacent the containers must be heated, and much of the heat is not utilized for heating the seals. Further, it is relatively difficult to maintain a uniform minimum temperature over the entire heated area. Still another shortcoming lies in the difficulty in adjusting the device to accommodate containers of differing heights which often can vary as much as four inches. Still another shortcoming lies in the absence of provision for sensing the failure of one or more functions of the device while it is continuously in operation, resulting in the production of defectively sealed containers, or containers passing through the device without seals.